Just replaced the top end on a 305 with stock cast heads and an aluminum intake, Everything works fine run it around town for a few days it is all good. Take it out on the hiway and run it a little hard and I get a vacuum leak. This is the second intake and have tried gaskets from Mr. Gasket and Fel-Pro. New PCV valve and two breathers on the valve covers passenger side all new. I need help, getting real good at installing an intake but didn't want to.